Self-developed Rollei film and a question

Some time ago I bought a couple of rolls of Rollei Retro 80S to try out. Last weekend I finally developed and scanned them and here some results.

As you may have noticed some of the photos turned out very contrasty, while others are really fine. And there were some really gruesome results as well, on which later down the road. Both rolls were developed together so the reason for such an outcome escapes me. I’ve got a couple of ideas, though, and an old developer is one of them. After developing these two rolls it turned yellow, and I’ve read that it might be the sign it’s gone.

Both rolls were developed together so the reason for such an outcome escapes me. I’ve got a couple of ideas, though, and an old developer is one of them. After developing these two rolls it turned yellow, and I’ve read that it might be the sign it’s gone.

Another reason is wrong agitation time or/and speed. I’m still learning to develop film, and moreover, this time I used my new dev tank, so maybe I agitated too fast or something. And there was also a moment when I started agitating without setting my timer right, so somewhere in the process, I could have agitated the rolls with less interval than recommended. It doesn’t explain those fine results but I couldn’t come up with any other theory.

Whatever the reason the negatives came out so transparent in some frames that my scanner had troubles defining the limits. It skipped one or two completely and cropped a little bit some more. I managed to save a couple of photos from oblivion and they look like this.

Any ideas why the photos turned out so contrasty and transparent? What did I do wrong?